4 DNA extraction and quantification
DNA extraction has two main aims: firstly, to be very efficient, extracting enough DNA from a sample to perform the DNA profiling – this is increasingly important as the sample size diminishes – and secondly, to extract DNA that is pure enough for subsequent analysis – the level of difficulty here depends very much on the nature of the sample. Once the DNA has been extracted quantifying the DNA accurately is important for subsequent analysis.
There are many methods available for extracting DNA. The choice of which method to use depends on a number of factors, including the sample type and quantity; the speed and in some cases ability to automate the extraction procedure [1-4]; the success rate with forensic samples, which is a result of extracting the maximum amount of DNA from a sample and at the same time removing any PCR inhibitors that will prevent successful profiling [1, 5, 6]; the chemicals that are used in the extraction – most laboratories go to great lengths to avoid using hazardous chemicals; and the cost of the procedure. Another important factor is the experience of the laboratory staff.
General principles of DNA extraction
The three stages of DNA extraction can be classified as (i) disruption of the cellular membranes, resulting in cell lysis, (ii) protein denaturation, and finally (iii) the sepa- ration of DNA from the denatured protein and other cellular components. Some of the extraction methods commonly used in forensic laboratories are described below.
Chelex® 100 resin
The Chelex® 100 method was one of the first extraction techniques adopted by the forensiccommunity.Chelex® 100isaresinthatiscomposedofstyrene-divinylbenzene
An Introduction to Forensic Genetics W. Goodwin, A. Linacre and S. Hadi
© 2007 John Wiley & Sons, Ltd